DF4 Flashcards
What is energy density?
The amount of energy per kilogram of fuel.
What is a chemical bond?
Electrical attraction between atoms or ions.
What is bond enthalpy (bond dissociation enthalpy)?
The energy needed to break one mole of a bond to give separate atoms (all in the gaseous state).
Is bond breaking endo/exothermic?
Endothermic - so positive value.
What is the average bond enthalpy?
The average quantity of energy needed to break a particular bond.
What is the relationship between the number of bonds and bond enthalpy?
As the number of bonds increase (e.g. single to double to triple), the bond enthalpy increases as well.
What is the relationship between the bond lengths and bond enthalpies?
As bond length decreases, bond enthalpy increases (as attraction increases).
How are bond enthalpies usually measured?
Measured indirectly using enthalpy cycles.
Why are bond enthalpies measured using enthalpy cycles?
- Isn’t easy to measure enthalpies as there is more than one type of bond in a compound.
- Difficult to make measurements when everything is in gaseous state.
Is bond-making endo/exothermic?
Exothermic - so negative value.
Is it necessary to break all bonds in a reaction?
No because as soon as the first of the old bonds are broken, new bonds start forming. This releases enough energy to keep the reaction going.
